In the past, estimates of water requirements of floodplain trees were based on past hydrology and inundation trends rather than quantitative measurements to understand how trees use water (when, where from in the soil profile) and the drivers of tree condition. During the Millennium Drought, more than 70% of iconic red gum stands in the Murray-Darling Basin were in poor health or dead. Environmental flows were considered as a way to improve tree health however there was little information on how effective this would be and how much water would be required, what season and for how long.
The development of the Murray-Darling Plan, a Plan to equitably share water between users and the environment, required research to understand how to manage floodplain vegetation in the future with limited water resources, especially during drought periods. Information to inform delivery of environmental flows is critical to ensure that water is used to its maximum potential to benefit both users and the environment.
CSIRO provides experienced, demonstrated long-term expertise in vegetation water use and tree ecohydrology. It also has the ability to ensure that rigorous science in the fieldwork domain is undertaken by ensuring appropriate instrumentation sample size is used to provide the most robust results. Expertise crosses terrestrial, marine and riparian zones. Multi-disciplinary research is undertaken through collaboration with scientists in complimentary fields internal and external to CSIRO, to maximise research outcomes.
Science and Innovation
Project design and data collection in floodplain environments requires innovation to ensure success in the natural world. Often floodwater cannot be provided to high elevation vegetation and alternate ways to deliver water must be considered and trailed. New technology is applied when available to add value to existing techniques and push the boundary of what we currently understand in relation to vegetation water requirements and response to flooding to inform water resource management. Field installed sapflow sensors underpin the studies within this work package to determine tree water use and the response of vegetation to water made available through natural floods or via environmental watering methods.
A collection of studies over several years has been completed by CSIRO to improve field understanding of vegetation condition, water use and water requirements and response of vegetation to various innovative watering techniques and overbank flooding. It is a package of work that aimed to provide quantified knowledge to inform water requirements of vegetation within the Murray-Darling Basin and tools to assist with monitoring of vegetation condition over time. The impact of this work continues to evolve but recognition is given to its value with invitations to CSIRO to provide expert knowledge to several committees involved in developing environmental water resource plans.
This rigorous work package has been important to continue the evolution of the Murray-Darling Basin Plan with respect to understanding vegetation water requirements and how much and when environmental water is required to prevent significant decline. Some key project outcomes include:
- Past estimates of Red Gum water requirements have been based on spatial observations. A large field study, the first of its kind, conclusively quantified the water use and requirements of Red Gums.
- Artificial flooding methods are required to ameliorate vegetation water stress during drought periods. Creation of an innovative freshwater lens was shown to be an effective method to improve vegetation condition.
- Spatial analysis was important to show that floodplain vegetation respond positively to elevated weir pool levels related to flooding and delivery of irrigation water during summer months.
- One study using drip irrigation, demonstrated the response of drought stressed Black Box to an environmental flow. New thresholds to water required to improve tree conditions were discovered.
- Doody TM, Colloff MJ, Davies M, Koul V, Benyon RG, Nagler PL. 2015. Quantifying water requirements of riparian river red gum (Eucalyptus camaldulensis) in the Murray-Darling Basin, Australia – implications for the management of environmental flows. Ecohydrology. 8(8), 1471-1487.
- Doody TM, Benger S, Overton IC, Pritchard J. 2014. Ecological response of Eucalyptus camaldulensis (River Red Gum) to extended drought and flooding along the River Murray, South Australia, 1997-2011. Australian Journal of Marine and Freshwater Research, 65(12), 1082-1093.
- Doody TM, Glenn EP, Benyon RG. 2013. Transpiration and stomatal conductance trends in riparian vegetation. Acta Horticulturae, 991, 171-179.
- Doody TM, Holland KL, Benyon RG, Jolly ID. 2009. Effect of groundwater freshening on riparian vegetation water balance. Hydrological Processes, 23(24): 3485-3499.
The Vegetation Theme will evaluate the contribution of Commonwealth environmental water to the diversity and condition of non-woody vegetation across the Murray- Darling Basin, as well investigate how to best use it to achieve environmental outcomes for tree species such as River red gum and Black box.